The present invention relates to a rotary printing machine for printing several colours on continuously fed sheets.
Printing machines are already known for printing several colors on sheets, particularly on cardboard sheets, these printing machines comprising a plurality of printing units corresponding to the different colors. These printing machines have the major drawback that, when it is desired to modify the format of the print, they necessitate a change of equipment i.e. the cylinders, which takes up a relatively long period of time. In the case of printing short series, i.e. comprising a relatively low number of printed sheets of the same format, the time required for replacing equipment may be equal to the time for actually printing the series in question.
To reduce the time necessary for changing equipment, during which the printing machine is immobilized, it has already been envisaged to produce machines in which the impression cylinders, and more particularly for each color, the blanket cylinder and the plate cylinder in the case of an offset printing machine, are mounted on the same frame which is transversely movable with respect to the framework of the machine. It is thus possible, in the case of a change of format, to replace the whole of a frame previously in operation with cylinders corresponding to the previously used format, by another similar frame, waiting outside the machine and carrying cylinders corresponding to the new format which has to be used. This arrangement requires, however, the provision of as many frames and consequently as many groups of pairs of cylinders as there are formats envisaged for printing. It is obvious that such a solution is particularly expensive.